Organotin unsymmetric dithiocarbamates: Synthesis, formation and characterisation of tin(II) sulfide films by atmospheric pressure chemical vapour deposition

Article abstract of DOI:10.1016/S0277-5387(01)00908-1

A series of tin unsymmetric dithiocarbamate complexes have been made from metathesis reaction of [CH₃(C₄H₉)NSC₂]Li and R_nSnCl_4-n; [R_nSn(S₂CN(C₄H₉)CH₃) _4-n] [n = 3, R = Me (1), Bu (2), Ph (3); n = 2, R = Me (4), Bu (5), Ph (6); n = 1, R = Me (7), Bu (8), Ph (9)]. The complexes were characterised by microanalysis, ¹³C, ¹H and ¹¹⁹Sn NMR, M?ssbauer and, in the case of 3, by X-ray diffraction, which revealed one short Sn-S [2.4631(9) ?] and one long Sn-S interaction [3.084(1) ?] indicative of a weakly chelating dithiocarbamate ligand. Atmospheric pressure chemical vapour deposition using 1 and 8 with H₂S at 350-550 °C produced SnS and Sn₂S₃ films on glass substrates. The tin sulfides were analysed by Raman, EDAX, SEM and band gap measurements. Growth rates were of the order of 150 nm min^-1.

Full text of DOI:10.1016/S0277-5387(01)00908-1

Polyhedron 20 (2001) 2989–2995
www.elsevier.com/locate/poly
Organotin unsymmetric dithiocarbamates: synthesis, formation and
characterisation of tin(II) sulfide films by atmospheric pressure
chemical vapour deposition
A.T. Kana a, T.G. Hibbert a, M.F. Mahon a, K.C. Molloy a,*, I.P. Parkin b, L.S. Price b
a Department of Chemistry, Uni6ersity of Bath, Cla6erton Down, Bath, BA2 7AY, UK
b Department of Chemistry, Uni6ersity College London, 20 Gordon Street, London, WC1H OAJ, UK
Received 24 May 2001; accepted 13 August 2001
Abstract
A series of tin unsymmetric dithiocarbamate complexes have been made from metathesis reaction of [CH3(C4H9)NSC2]Li and
RnSnCl4−n; [RnSn(S2CN(C4H9)CH3)4−n] [n=3, R=Me (1), Bu (2), Ph (3); n=2, R=Me (4), Bu (5), Ph (6); n=1, R=Me (7),
1
Bu (8), Ph (9)]. The complexes were characterised by microanalysis, 13C, H and 119Sn NMR, Mo¨ssbauer and, in the case of 3,
,
,
by X-ray diffraction, which revealed one short SnꢀS [2.4631(9) A] and one long SnꢀS interaction [3.084(1) A] indicative of a
weakly chelating dithiocarbamate ligand. Atmospheric pressure chemical vapour deposition using 1 and 8 with H2S at 350–550
°C produced SnS and Sn2S3 films on glass substrates. The tin sulfides were analysed by Raman, EDAX, SEM and band gap
measurements. Growth rates were of the order of 150 nm min−1. © 2001 Published by Elsevier Science Ltd.
Keywords: Tin; Dithiocarbamates; Thin film; APCVD; X-ray structures
with one tin atom being six coordinate and the other
atom three coordinate [8]. All of the tin sulfides show
interesting optical spectra and semiconducting proper-
ties; SnS2 has a band gap of 2.07–2.18 eV (depending
on exact poly-type) and is an n-type semiconductor [9],
Sn2S3 is a direct forbidden semiconductor with a band
gap of 0.95 eV and has highly anisotropic conduction
[10], while SnS can act as either an n-type or p-type
conductor (dependent on minor stoichiometry varia-
tions) and typically has a band gap of 1.3 eV, although
values from 1.08 to 1.51 eV have been reported [11]. All
of the tin sulfides have excited interest as semiconduc-
tors although SnS has elicited most attention as its
electronic band gap of 1.3 eV is midway between silicon
and GaAs [12] and as such has potential applications in
solar cells and holographic recording media [13,14].
Tin–sulfide thin-films have received scant attention
compared to the extensive thin-film technology of sili-
con and gallium arsenide. Chemical baths have been
used to deposit a range of tin sulfide films [15]. A bath
containing SnCl2, Na2S2O3 and EDTA in aqueous solu-
tion has been used to deposit SnS on glass and titanium
1. Introduction
Tin sulfide has three main phases: SnS and SnS2 that
exhibit layer structures and mixed valence Sn2S3 that
forms a ribbon structure [1]. Tin(II) sulfide consists of a
distorted rock salt structure which is isostructural with
germanium sulfide; six sulfur atoms surround each tin
atom with three short SnꢀS bonds within the layer and
three long bonds formed to sulfur atoms in the next
layer [2,3]. Tin(II) sulfide has found application as a
solid-state lubricant [4,5]. Tin(IV) sulfide is isostructural
with CdI2; each tin atom is octahedral with three sulfur
atoms above and below; weak SꢀS interactions between
the SnS2 sheets [6,7] also make this material a useful
lubricant [4,5]. It has in excess of 70 poly-type struc-
tures dependent on the overlap of the sulfur–sulfur
sheets. Ditin trisulfide is a type I mixed valence Sn(II)/
Sn(IV) compound which has a similar local order to the
other tin sulfides, however it exhibits a ribbon structure,
* Corresponding author. Tel.: +44-1225-826-382; fax: +44-1225-
826-231.
E-mail address: chskcm@bath.ac.uk (K.C. Molloy).
0277-5387/01/$ - see front matter © 2001 Published by Elsevier Science Ltd.
PII: S0277-5387(01)00908-1

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A.T. Kana et al. / Polyhedron 20 (2001) 2989–2995
substrates [16]. A related solution of SnCl2, ammonia,
thioacetamide and glacial acetic acid has been used to
grow SnS films on the sides of suspended glass slides at
75 °C [17]. A dipping method has been used to form tin
sulfide films by immersing glass slides into alternate
solutions containing Na2S and SnCl2 [18]. Tin(IV)
sulfides have also been grown by dip-coating [19]. The
tin–sulfide films produced from chemical baths showed
the presence of significant impurities, are poorly adhe-
sive and required post-treatment to produce a crys-
talline film [20]. Improved tin sulfide films have been
grown at the anode in cyclic voltammetry experiments
[21] and from spray-pyrolysis using SnCl2 and
dimethylthiourea [22]. Deposition methods from the gas
phase have included limited examples of low pressure
[23] and plasma assisted chemical vapour deposition
(CVD) [14]. Plasma enhanced CVD reaction of SnCl4
and H2S at 100–350 °C produced SnS films on small
silica substrates that were contaminated with chlorine
and elemental sulfur. Organometallic precursor routes
to tin sulfide films on CaF2 substrates were reported by
reaction of tetraalkyltin species with hydrogen sulfide
and hydrogen at 600 °C, although the materials were
only characterised by thickness measurements and
colour. The authors speculated that SnS formed be-
cause of the reducing conditions employed in the exper-
iment [23].
all of these single source systems failed to deposit tin
sulfides in the absence of H2S. This failure was tracked
to a facile disulfide (RS–SR) elimination pathway.
Subsequent molecular orbital calculations and an ex-
tensive literature search has revealed that the general
class of [M(SR)4] (M=Group IV) molecules suffer
significant distortions from tetrahedral geometry be-
cause of non-covalently bonded S···S interactions. This
distortion and cis-annular interaction promotes the
disulfide elimination pathway [30]. It should be noted
that all of the single source precursors could be made to
deposit tin(II) sulfide coatings by employing a minimal
flow of H2S in the system.
In the search for new single-source precursors to tin
sulfide films we report here the synthesis, characterisa-
tion and APCVD of unsymmetric tin dithiocarbamate
derivatives. The dithiocarbamate ligands provide direct
SnꢀS bonds and would be expected not to undergo an
elimination pathway as readily because of the chelate
effect. Our interest in the usage of these ligands extends
from the extensive work of O’Brien on the deposition
of II–VI films [31] where it was noted that unsymmetri-
cal dithiolates are significantly more volatile than the
symmetric analogues.
2. Experimental
We have instituted an intensive study of tin sulfide
films on glass substrates by atmospheric pressure and
aerosol assisted CVD. Reaction of tin tetrahalides with
H2S under atmospheric pressure chemical vapour depo-
sition (APCVD) conditions provided a facile route to
high-quality, phase-pure, uniform, conformal tin
sulfides on glass-substrates [24–26]. The tin sulfides
deposited in the experiments were directly related to the
temperature of the substrate and were largely invariant
of the precursor concentration. At 300–500 °C single
phase SnS2 was deposited; at 525 °C Sn2S3 formed
whilst at 550 °C and above single phase SnS was
observed. Growth rates under optimum conditions were
in excess of 1 mm min−1. We have expanded this study
to other tin sources and dual-source reactions involving
organotin carboxylates [Bu3SnO2CCF3] [27] from which
only one phase of tin sulfide, SnS, was produced at
300–550 °C.
2.1. General
Manipulations were carried out under an atmosphere
of dry N2. [CH3(C4H9)NSC2]Li was prepared as de-
scribed previously [32]. Methylene chloride was dried
by distillation over CaH2. All other solvents and
reagents were obtained commercially and used without
further purification. All NMR spectra were recorded as
saturated CDCl3 solutions at room temperature on a
JEOL 270MHz spectrometer. Chemical shifts are in
ppm with respect to Me4Si (1H, 13C) or Me4Sn (119Sn);
coupling constants in Hz. Details of our Mo¨ssbauer
spectrometer and related procedures are given else-
where [33]. Isomer shift (IS), quadrupole splittings (QS)
and full width at half height (Y) are in mm s−1 and
were measured at 78 K.
The next goal was to produce single-source precur-
sors to tin sulfide coatings. A range of volatile precur-
sors such as [Sn(SCH2CF3)4] and [Sn(SPh)4] were
investigated [28,29]. These homoleptic materials contain
an all-sulfur primary co-ordination-sphere and would
be expected to form tin sulfides under CVD conditions.
This is a precursor strategy that is at the heart of all
single-source CVD studies and enshrines a molecular
Achilles heel within the molecule that on decomposition
in the gas phase will form the required coating by
maintaining the metal–element bond. Unfortunately,
2.2. Synthesis of organotin dithiocarbamates
2.2.1. Generalised route using solid organotin starting
materials
The organotin reagent and the appropriate stoichio-
metric amount of [CH3(C4H9)NSC2]Li were placed in a
dry Schlenk tube against an N2 counter-flow. CH2Cl2
(50 ml) was then added and the reagents were stirred at
room temperature for 16 h. LiCl was removed by
filtration and the solvent was removed in vacuo. Re-
crystallisations were from Et2O.

A.T. Kana et al. / Polyhedron 20 (2001) 2989–2995
2991
2.2.2. [Me3Sn(S2CN(CH3)C4H9)] (1)
2.3.1. [nBu3S([S2CN(CH3)C4H9)] (2)
Orange oil, 85% yield, microanalysis (required for
C9H21SN2Sn): C, 33.3 (33.2); H, 6.5 (6.5); N, 4.3 (4.3);
1H NMR: 0.59 [9H, s, 2J(119,117SnH)=57.2, 52.0,
SnCH3], 0.95 (3H, t, J=7.3, Bu CH3), 1.35 (2H, m,
J=7.7, CH2), 1.69 (2H, p, J=7.0, CH2), 3.40 (3H, s,
NCH3), 3.87 (2H, t, J=7.3, NCH2); 13C NMR: 0.6
Yellow oil, 60% yield, microanalysis (required for
C18H39NS2Sn); C, 47.7 (47.8); H, 8.7 (8.7); N, 3.3 (3.1);
1H NMR: 0.84 (9H, t, J=7.3, Bu CH3), 0.88 (3H, t,
J=7.3, Bu CH3), 1.24 (6H, m, J=7.3, CH2), 1.26 (6H,
m, J=7.3, CH2), 1.29 (2H, m, J=7.3, CH2), 1.56 (6H,
m, J=7.5, CH2), 1.62 (2H, m, J=9.1, CH2), 3.34 (3H,
s, NCH3), 3.82 (2H, t, J=7.7, NCH2); 13C NMR: 13.7
(Bu CH3), 14.0 (Bu CH3), 19.9 [SnCH2,
1J(119,117SnC)=322 unresolved], 26.3 (CH2), 28.5
(CH2), 28.9 (CH2), 34.2 (SnCH2), 42.3 (NCH3), 56.9
(NCH2), 200.4 (CN); 119Sn NMR: 21.0; Mo¨ssbauer: IS
1.39, QS 2.19, Y 0.96.
1
[SnCH3, J(119,117SnC)=382, 366], 15.3 (Bu CH3), 21.5
(CH2), 30.5 (CH2), 44.6 (NCH3), 58.9 (NCH2), 198.7
(CN); 119Sn NMR: 22.1; Mo¨ssbauer: IS 1.27, QS 2.14,
Y 1.00.
2.2.3. [Ph3Sn(S2CN(CH3)C4H9)] (3)
White solid, 93% yield, m.p. 87–88 °C, microanalysis
2.3.2. [nBu2Sn(S2CN(CH3)C4H9)2] (5)
(required for C24H27NS2Sn): C, 56.0 (56.3); H, 5.4 (5.3);
N, 2.7 (2.7); H NMR: 0.77 (3H, t, J=7.2, Bu CH3),
1
Orange oil, 66% yield, microanalysis (required for
C20H42N2S4Sn); C, 43.1 (43.1); H, 7.6 (7.6); N, 5.0 (5.0);
1H NMR: 0.87 (6H, t, J=7.2, Bu CH3), 0.89 (6H, t,
J=7.2, Bu CH3), 1.32 (4H, m, CH2), 1.35 (4H, m,
CH2), 1.63 (4H, m, J=7.5, CH2), 1.84 (4H, m, CH2),
1.95 (4H, m, CH2), 3.32 (6H, s, NCH3), 3.78 (4H, t,
J=7.7, NCH2); 13C NMR: 13.4 (Bu CH3), 13.5 (Bu
CH3), 17.4 [SnCH2, 1J(119,117SnC)=334 unresolved],
19.7 (CH2), 26.8 (CH2), 28.6 (CH2), 28.9 (CH2), 42.7
(NCH3), 57.1 (NCH2), 198.2 (CN); 119Sn NMR: −
341.3; Mo¨ssbauer: IS 1.52, QS 2.89, Y 0.92.
1.05 (2H, m, J=7.5, CH2), 1.32 (2H, m, J=7.7, CH2),
2.89 (3H, s, NCH3), 3.41 (2H, t, J=7.5, NCH2), 7.28
(9H, m, ArH), 8.07 (6H, d, J=7.9, ArH); 13C NMR:
14.1 (Bu CH3), 20.4 (CH2), 29.4 (CH2), 43.5 (NCH3),
58.7 (NCH2), 129.3 (ArC), 129.7 (ArC), 137.6 (ArC),
148.2 (ArC), 196.5 (CN); 119Sn NMR: −190.0; Mo¨ss-
bauer: IS 1.23, QS 1.79, Y 1.05.
2.2.4. [Me2Sn(S2CN(CH3)C4H9)]2 (4)
White solid, 89% yield, m.p. 88–89 °C, microanalysis
(required for C14H30N2S4Sn): C, 33.5 (33.5); H, 6.4
1
(6.4); N, 6.0 (5.9); H NMR: 0.81 (6H, t, J=7.2, Bu
2.3.3. [MeSn(S2CN(CH3)C4H9)3] (7)
Yellow solid, 62% yield, m.p. 72–73 °C, microanaly-
CH3), 1.11 (4H, m, J=7.7, CH2), 1.40 (4H, p, J=7.5,
2
CH2), 1.94 [6H, s, J(119,117SnꢀH)=86.4, 82.8, SnCH3],
sis (required for C19H39N3S6Sn); C, 36.5 (36.8); H, 6.5
2.98 (6H, s, NCH3), 3.52 (4H, t, J=7.7, NCH2); 13C
NMR: 14.2 (Bu CH3), 16.5 (SnCH3) 20.4 (CH2), 29.4
(CH2), 42.3 (NCH3), 57.1 (NCH2), 200.8 (CN); 119Sn
−349.2; Mo¨ssbauer: IS 1.40, QS 2.89, Y 0.90.
1
(6.3); N, 6.5 (6.8); H NMR: 0.88 (9H, t, J=7.0, Bu
CH3), 1.28 (6H, m, J=7.8, CH2), 1.64 (6H, m, J=7.4,
2
CH2), 1.85 [3H, s, J(119,117SnH)=59.3, 57.4, SnCH3],
3.29 (9H, s, NCH3), 3.69 (6H, t, J=7.4, NCH2); 13C
NMR: 14.1 [SnCH3], 14.3 (Bu CH3), 20.4 (CH2), 29.3
(CH2), 43.5 (NCH3), 58.4 (NCH2), 201.1 (CN); 119Sn
NMR: −605.2 (53%), −780.5 (100%); Mo¨ssbauer IS
1.13, QS 1.92, Y 1.18.
2.2.5. [Ph2Sn(S2CN(CH3)C4H9)2] (6)
White solid, 94% yield, m.p. 121–122 °C, microanal-
ysis (required for C24H34N2S4Sn): C, 48.3 (48.2); H, 5.7
1
(5.7); N, 4.7 (4.7); H NMR: 0.93 (6H, t, J=7.3, Bu
CH3), 1.33 (4H, m, J=7.5, CH2), 1.68 (4H, m, J=7.5,
CH2), 3.31 (6H, s, NCH3), 3.73 (4H, t, J=7.7, NCH2),
7.28 (6H, m, J=7.7, ArH), 8.07 (4H, d, J=7.7, ArH);
13C NMR: 13.7 (Bu CH3), 19.9 (CH2), 28.9 (CH2), 43.3
(NCH3), 58.3 (NCH2), 128.1 (ArC), 128.3 (ArC), 134.2
(ArC), 151.7 (ArC), 199.2 (CN); 119Sn −505.3; Mo¨ss-
bauer: IS 1.26, QS 2.31, Y 1.20.
2.3.4. [nBuS([S2CN(CH3)C4H9)3] (8)
White solid, 51% yield, microanalysis (required for
C22H45N3S6Sn); C, 39.3 (39.9); H, 6.7 (6.9); N, 6.2 (6.3);
1H NMR: 0.79 (9H, t, J=7.1, Bu CH3), 1.01 (3H, t,
J=7.3, Bu CH3), 1.10 (6H, m, J=7.7, CH2), 1.40 (6H,
m, J=7.3, CH2), 1.58 (2H, m, J=7.3, CH2), 1.87 (2H,
m, CH2), 2.49 (2H, m, SnCH2), 2.92 (9H, s, NCH3),
3.44 (6H, t, J=7.7, NCH2); 13C NMR: 14.2 (Bu CH3),
14.5 (Bu CH3), 20.4 [SnCH2], 26.1 (CH2), 29.4 (CH2),
30.4 (CH2), 34.7 (CH2), 42.9 (NCH3), 58.2 (NCH2),
192.8 (CN); 119Sn NMR: −580.2 (48%), −807.0
(100%); Mo¨ssbauer: IS 1.25, QS 1.84, Y 1.04.
2.3. Generalised route using liquid organotin starting
materials
[CH3(C4H9)NSC2]Li [32] was suspended in CH2Cl2
(50 ml) in a Schlenk tube. The appropriate stoichiomet-
ric amount of the organotin reagent was then added via
syringe and the reagents were stirred at room tempera-
ture for 16 h. Nascent LiCl was removed by filtration
and the solvent was removed in vacuo. Recrystallisa-
tions were from Et2O.
2.3.5. [PhSn(S2CN(CH3)C4H9)3] (9)
Pale yellow solid, 76% yield, m.p. 128–130 °C, mi-
croanalysis (required for C24H41N3S6Sn); C, 42.1 (42.2);
1
H, 6.0 (6.1); N, 6.2 (6.2); H NMR: 0.94 (9H, t, J=6.2,

2992
A.T. Kana et al. / Polyhedron 20 (2001) 2989–2995
,
Bu CH3), 1.35 (6H, m, J=7.3, CH2), 1.71 (6H, m,
J=5.5, CH2), 3.34 (9H, s, NCH3), 3.71 (6H, t, J=7.1,
NCH2), 7.36 (3H, m, ArH), 7.97 [2H, d, 3J=7.9,
2J(119SnH)=37.7, ArH); 13C NMR: 13.8 (Bu CH3),
19.9 (Bu CH2), 28.9 (Bu CH2), 43.2 (NCH3), 58.3
(NCH2), 128.9 (ArC), 130.7 (ArC), 131.5 (ArC), 150.8
(ArC), 191.7 (CN); 119Sn NMR: −654.6 (100%),
−834.1 (45%); Mo¨ssbauer: IS 1.11, QS 1.81, Y 0.82.
and −0.271 e A−3, respectively. The asymmetric unit,
shown in Fig. 1 along with the labelling scheme used
selected metrical data, and was produced using ORTEX
[36].
Crystals of [PhSn(S2CN(CH3)C4H9)3] (9) were also
grown and belong to the triclinic crystal class (a=
9.202, b=10.901, c=17.039 A; h=103.055, i=93.97,
k=108.151°). Although the heavy atom framework of
the molecule was evident, no complete molecular model
was refineable in either triclinic space group suggesting
some subtle form of crystal twinning.
,
2.4. X-ray crystallography
A crystal of 3 of approximate dimensions 0.25×
0.25×0.20 mm was used for data collection. Crystal
data: C24H27NS2Sn, M=512.28, triclinic, a=9.837(2),
2.5. Chemical 6apour deposition studies
,
b=9.896(2), c=14.140(3) A, h=72.73(2), i=
Nitrogen (99.99%) and H2S (99.9%) were obtained by
BOC and used as supplied. Coatings were obtained on
glass coated with a SiCO barrier layer that inhibited
diffusion of ions from the glass. Atmospheric pressure
CVD experiments were conducted on 225×89×4 mm
pieces using a horizontal bed cold wall APCVD reactor.
The glass was cleaned by washing with petroleum ether
(60–80) and isopropanol and air-dried prior to use. The
glass was heated by a flat-bed graphite block that
contained three Whatman cartridge heaters. The tem-
perature of the graphite block was monitored by a
Pt–Rh thermocouple. Thermocouple measurements in-
dicated that temperature gradients of less than 5 °C at
500 °C were noted across glass substrates. All gas
handling lines, regulators and flow valves were made of
stainless steel and were 1/4’’ internal diameter except
3
,
72.04(2), k=68.81(2)°, U=1193.9(4) A , space group
P1 (No.2), Z=2, Dcalc=1.425 g cm−3, m(Mo Ka)=
1.254 mm−1, F(000)=520. Crystallographic measure-
ments were made at 293(2) K on a CAD4 automatic
four-circle diffractometer in the range 2.26BqB
24.97°. Data (4583 reflections) were corrected for
Lorentz and polarization but not for absorption. In the
final least-squares cycles all atoms were allowed to
vibrate anisotropically. Hydrogen atoms were included
at calculated positions where relevant.
The solution of the structure (SHELX86) [34] and
refinement (SHELX93) [35] converged to a conventional
[i.e. based on 3576 F2 data with Fo\4|(Fo)] R1=
0.0206 and wR2=0.0531. Goodness-of-fit=0.965. The
maximum and minimum residual densities were 0.319
Fig. 1. The asymmetric unit of 3 showing the labelling scheme used in the text and tables. Thermal ellipsoids are at the 30% probability level.
Selected metrical data: Sn(1)ꢀC(1) 2.152(2), Sn(1)ꢀC(7) 2.130(2), Sn(1)ꢀC(13) 2.148(2), Sn(1)ꢀS(1) 2.4631(9), Sn(1)ꢀS(2) 3.084(1), S(1)ꢀC(19)
,
1.753(3), S(2)ꢀC(19) 1.668(3) A; C(7)ꢀSn(1)ꢀC(1) 108.42(9), C(13)ꢀSn(1)ꢀC(1) 105.28(9), C(7)ꢀSn(1)ꢀC(13) 114.50(9), C(1)ꢀSn(1)ꢀS(1) 89.47(6),
C(7)ꢀSn(1)ꢀS(1) 115.31(6), C(13)ꢀSn(1)ꢀS(1) 119.42(6), C(1)ꢀSn(1)ꢀS(2) 152.13(7)°.

A.T. Kana et al. / Polyhedron 20 (2001) 2989–2995
2993
for the inlet to the mixing chamber and the exhaust line
from the apparatus, which were 1/2’’ i.d. In these
experiments three gas lines were used; two for nitrogen
and one for a nitrogen/hydrogen sulfide line. The gases
came directly from cylinders. Gas flows were adjusted
using suitable regulators (spectrol 50S for the H2S line)
and flow controllers. The exhaust from the reactor was
vented directly into the extraction system of a fume
cupboard. All of the apparatus was baked out with
plain nitrogen at 150 °C for 3 h before and after the
runs. Deposition experiments were conducted by heat-
ing the horizontal bed reactor to the required tempera-
tures before diverting one of the nitrogen lines through
the bubbler and hence to the reactor. Bubbler tempera-
tures were set at 82–88 °C for [SnMe3(S2CNMeBu)]
and 110–135 °C for [SnBu(S2CNMeBu)3]. Deposition
experiments were timed by stop-watch and were typi-
cally for 3 min. The precursors were mixed with a
nitrogen diluted H2S flow 1 cm before the mixing
chamber of the coater (a full description of the APCVD
apparatus used can be found in a previous paper [24]).
At the end of the deposition the bubbler line was closed
and only plain nitrogen passed over the substrate. The
glass substrate was allowed to cool with the graphite
block to approximately 60 °C before it was removed.
Coated substrates were handled and stored in air. The
large coated glass sample was broken up into approxi-
mately 1×1 cm squares for subsequent analysis by
EDAX, SEM and UV studies. Large pieces of glass (ca.
4×4 cm) were used for sheet resistance, X-ray powder
diffraction, Raman and Scotch tape tests.
(1)
Compounds 3, 4, 6–9 are low melting point solids
(80–125 °C) while compounds 1, 2 and 5 are oils.
Yields were in the range 51–94% and generally decrease
as the degree of substitution increases. All species are
air-stable and soluble in common organic solvents. All
of 1–9 had satisfactory microanalytical data and the
expected H and 13C NMR spectra; typical 1,2J cou-
plings were observed, for example showed
1
1
1J(119,117SnC)=382, 366 Hz and J(119,117SnH)=57.2,
52.0 Hz. Mo¨ssbauer data for the series of monoorgan-
otin compounds (7–9) (quadrupole splittings (qs):
1.81–1.92 mm s−1) are uninformative as the regions
associated with coordination number=4 (1.3–2.1 mm
2
s
−1), 5 (1.6–2.4 mm s−1) and 6 (1.6–2.4 mm s−1) are
all very similar. Data for the triorganotin compounds
1–3 (qs: 1.79–2.19 mm s−1) are consistent with essen-
tially tetrahedral coordination about the metal (1.5–2.8
mm s−1) while quadrupole splitting data for the
diorganotin species (2.31–2.89 mm s−1) reflect weakly
chelating dithiocarbamate groups [37]. 119Sn NMR
chemical shifts are more sensitive to coordination num-
ber than Mo¨ssbauer quadrupole splitting values, and
for each of the three series (n=3, l=21, 22, −190;
n=2, l= −341, −349, −505; n=1, l= −780,
−580, −834 ppm, for R=Me, Bu, Ph, respectively)
the shifts are upfield of purely tetrahedral analogues,
e.g. RnSn(SR)4−n [38]. Collectively these data are con-
sistent with some degree of chelation, albeit rather
weak, by the dithiocarbamate towards the metal. This
is consistent with the structure of 3 described below.
X-ray powder diffraction patterns were measured on
a Philips X-pert diffractometer using unfiltered Cu Ka
,
,
(u1=1.5045 A, u2=1.5443 A) radiation in the reflec-
tion mode using glancing incident angle. UV–Vis spec-
tra were recorded in the range 200–1000 nm using a
Shimadzu double beam instrument, band gaps were
calculated by the direct method. SEM/EDAX was ob-
tained on a Hitachi S570 instrument using the KEVEX
system. Raman spectra were acquired on a Renishaw
Raman System 1000 using a helium–neon laser of
wavelength 632.8 nm. The Raman system was cali-
brated against the emission lines of neon. Reflectance/
transmission optical spectra were determined on a Xeiss
miniature spectrometer.
3.2. Crystal structure of Ph3Sn[S2CN(CH3)C4H9] (3)
The structure of 3 is shown in Fig. 1. While numer-
ous tin–dithiocarbamate complexes are known [39],
this is the first structurally-characterised example of
which we are aware in which the ligand is unsymmetri-
cally substituted. The coordination about tin in 3 is
mid-way between tetrahedral and trigonal bipyramidal
due to a weakly chelating dithiocarbamate group.
Sn(1)ꢀS(2) is significantly longer [3.084(1) A] than
Sn(1)ꢀS(1) [2.4631(9) A] and the nominally axial sub-
stituents are far from linearly arranged
3. Results
3.1. Synthesis of tin dithiocarbamates
,
,
Mono-, di- and tri-organotin derivatives of the un-
symmetrical dithiocarbamic acid CH3(C4H9)NCS2H
were prepared by reaction of its lithium salt with the
appropriate organotin chloride (Eq. (1)).
[S(2)ꢀSn(1)ꢀC(1) 152.13(7)°]. The remaining groups
bonded to tin do, however, expand the angles subtend

2994
A.T. Kana et al. / Polyhedron 20 (2001) 2989–2995
at the metal towards the 120° expected of equatorial
substituents [114.50(9), 115.31(6), 119.42(6)°].
previous thin film measurements [24–26]. The Sn2S3
film was predominantly brown in colour, however the
edges of the film were yellow and Raman microscopy
measurements indicated that SnS2 was present. SEM
measurements showed that the SnS films had a wavy
agglomerated structure and the Sn2S3 material was
composed of interlocked needles and as such matched
those observed in previous APCVD experiments [24–
26]. Films were of the order of 300 nm thick. EDAX
analysis of all the films showed the presence of tin and
sulfur. Direct quantification was difficult as the films
were thin and the excitation voltage used produced
significant breakthrough to the underlying glass. The
films were too thin for quantification by X-ray diffrac-
tion. Band gap measurements gave a direct band gap of
1.20–1.25 eV for the SnS films.
Crystallographic studies of organotin compounds
containing one or more dithiocarbamates show that
these ligands are rarely symmetrically bound to the tin,
i.e. one SnꢀS bond is longer than the other [39–44].
The structure of 3 is directly comparable with that of
[Ph3Sn(S2CNEt2)] where the chelating CꢁS“Sn bond is
,
3.11 A [45]. Hall and Tiekink have shown how the
electron donating/withdrawing effect of the other lig-
ands bound to tin markedly affect both the aniso-
bidentate nature of the SnꢀS chelation (DSnꢀS) and the
solid state structure for compounds of the type
R2Sn(S2CNR%) (R=alkyl, aryl, vinyl, chloride; R%=
2 2
alkyl) [39]. We have recently reported the structures of
[BuSn(dtc)2Cl] and [BuSn(dtc)Cl2] (dtc=S2CNEt2) [46].
While crystals of the monoorganotin (9) were also
obtained, it proved impossible to locate and refine
adequately a complete molecular entity. The heavy
atom (Sn, S) framework was, however, clearly evident
and suggested a seven-coordinate pentagonal bipyrami-
dal geometry about tin.
4. Discussion
Tin unsymmetric dithiocarbamate complexes can be
readily made by metathetical exchange of a lithium salt
of a dithiocarbamic acid with an alkyltin chloride. The
complexes were low melting point solids or oils that
had sufficient vapour pressure to be used in APCVD
experiments. X-ray crystallographic studies of 3 showed
that the dithiocarbamate ligand was strongly bound
through one sulfur atom to the tin, with the second
sulfur atom only weakly bound. Hence the dithiocarba-
mate group was only weakly chelating. Tin NMR and
Mo¨ssbauer measurements were in agreement with each
dithiocarbamate ligand acting as essentially a uniden-
tate ligand with only a weakly chelating second sulfur.
APCVD experiments of 1 and 8 show that these
materials do not function as single-source precursors to
tin sulfide thin films. At temperatures up to 550 °C in
the absence of H2S, no coating could be obtained on
glass substrates. In the presence of a minimal flow of
H2S, SnS and Sn2S3 coatings could be grown. The
absence of a film without a secondary sulfur source is a
common feature of many APCVD systems we have
investigated [24–26,28,29]. In the case of homoleptic tin
thiolates this has been attributed to a facile disulfide
elimination mechanism, that generates tin–metal which
in turn can only form tin–sulfide in the presence of a
secondary sulfur source such as H2S. It was hoped that
the use of chelating ligands such as dithiocarbamates
would discourage a bis-ligand elimination pathway.
However, the unsymmetric dithiocarbamates deriva-
tives are essentially monodentate ligands with a weak
secondary interaction rather than strongly chelating
ligands, which may account for the lack of a film in the
absence of H2S. The formation of SnS films in the
majority of the CVD experiments in the presence of
H2S is analogous to previous work, indicative of a
3.3. Chemical 6apour deposition
APCVD using the two unsymmetrical dithiocarba-
mate precursors [SnMe3(S2CNMeBu)] (1) and
[SnBu(S2CNMeBu)3] (8) has been studied. In the ab-
sence of H2S no coating could be grown from either
precursor. The unsymmetrical dithiocarbamates were,
however, sufficiently volatile to give good carry over of
the precursor with bubbler temperatures set at 85 °C
for 1 and 110 °C for 8. In the presence of a minimal
flow of H2S (less than 1% of the gas stream), both
precursors produced grey tin(II) sulfide films at sub-
strate temperatures in excess of 500 °C. From 1 no
coating could be grown at a substrate temperature of
less than 350 °C. At 450 °C the coatings from 1 were
brown and consisted of Sn2S3 with a trace of SnS2. In
all of the depositions the coatings were only on the
leading edge of the glass and covered the first 4 cm of
the plate. Growth rates were at best approximately 150
nm min−1. This compares with growth rates of 1000
nm min−1 from equivalent reactions of SnCl4 and H2S.
3.4. Film characterisation
All the films formed from the APCVD of 1 or 8 with
minimal H2S flow passed the Scotch tape test. They
could however be readily abraded with a scalpel. The
film colours of grey for SnS and brown for Sn2S3 match
previous deposition studies [24–26]. Raman spectra
were very diagnostic showing bands at 307, 251, 234,
183 and 87 cm−1 for the Sn2S3 film and bands at 288,
220, 189, 163 and 96 cm−1 for the SnS films. The bands
exactly matched data for bulk Sn2S3 and SnS and

A.T. Kana et al. / Polyhedron 20 (2001) 2989–2995
2995
[15] R.D. Engleken, H.E. McCloud, C. Lee, M. Slayton, H. Goreishi,
J. Electrochem. Soc. 134 (1987) 2696.
[16] C.D. Lokhande, Mater. Chem. Phys. 28 (1991) 145.
[17] P. Pramanik, P.K. Basu, S. Biswas, Thin Solid Films 150 (1987)
269.
reduction of the metal centre [28,29]. It is also likely
that the sulfur in the growing films comes form the H2S
and not the dithiocarbamate precursor.
[18] M. Ristov, G. Sinadinovski, I. Grozdanov, M. Mitreski, Thin
Solid Films 173 (1989) 53.
5. Supplementary material
[19] A.J. Varkey, Int. J. Mater. Prod. Technol. 12 (1997) 490.
[20] V.V. Bhad, C.D. Iokhande, Bull. Electrochem. 7 (1991) 571.
[21] M.T.S. Nair, P.K. Nair, J. Semicond. Sci. Technol. 6 (1991) 132.
[22] A. Ortiz, S. Lopez, J. Semicond. Sci. Technol. 9 (1994) 2130.
[23] H.M. Manasevit, W.I. Simpson, J. Electrochem. Soc. 122 (1975)
444.
Crystallographic data for the structure have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 163857. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
[24] L.S. Price, I.P. Parkin, T.G. Hibbert, K.C. Molloy, Adv. Mater.
4 (1998) 222.
[25] L.S. Price, I.P. Parkin, A.M.E. Hardy, R.J.H. Clark, T.G.
Hibbert, K.C. Molloy, Chem. Mater. 11 (1999) 1792.
[26] I.P. Parkin, L.S. Price, A.M.E. Hardy, R.J.H. Clark, T.G.
Hibbert, K.C. Molloy, J. Phys. IV France 9 (1999) Pr8.
[27] L.S. Price, I.P. Parkin, M.N. Field, A.M.E. Hardy, R.J.H.
Clark, T.G. Hibbert, K.C. Molloy, J. Mater. Chem. 10 (2000)
527.
Acknowledgements
[28] G. Barone, T.G. Hibbert, M.F. Mahon, K.C. Molloy, L.S. Price,
I.P. Parkin, A.M.E. Hardy, M.N. Field, J. Mater. Chem. 11
(2000) 464.
[29] T.G. Hibbert, M.F. Mahon, K.C. Molloy, I.P. Parkin, L.S.
Price, J. Mater. Chem. 11 (2001) 469.
[30] T.G. Hibbert, M.F. Mahon, K.C. Molloy, I.P. Parkin, L.S.
Price, I. Silaghi-Dumitrescu, 2001, submitted for publication.
[31] M.R. Lazell, P. O’Brien, D.J. Otway, J.H. Park, Chem. Mater.
11 (1999) 3430.
[32] P. O’Brien, D.J. Otway, J.R. Walsh, Thin Solid Films 315 (1998)
57.
Dr D. Sheel and Dr K. Sandersen of Pilkington
Glass PLC are thanked for useful discussion and for
providing the reactor coater and undercoated glass for
deposition experiments. Mr D. Knapp and Mr D.
Morphett are thanked for help with construction of the
APCVD rig. The EPSRC are acknowledged for grants
GR/L54721 to K.C.M. and GR/L56442 and GR/
M82592 to I.P.P. Professor R.J.H. Clark is thanked for
help in acquiring the Raman spectra.
[33] K.C. Molloy, T.G. Purcell, K. Quill, I. Nowell, J. Organomet.
Chem. 267 (1984) 237.
[34] G.M. Sheldrick, SHELX 86S, A Computer Program for Crystal
Structure Determination, University of Go¨ttingen, Go¨ttingen,
Germany, 1986.
References
[35] G.M. Sheldrick, SHELX 93, A Computer Program for Crystal
Structure Refinement, University of Go¨ttingen, Go¨ttingen, Ger-
many, 1993.
[36] P. McArdle, J. Appl. Cryst. 28 (1995) 65.
[37] A.G. Davies, P.J. Smith, in: G. Wilkinson, F.G.A. Stone, E.W.
Abel (Eds.), Comprehensive Organometallic Chemistry, vol. 2,
Pergamon Press, Oxford, 1982, p. 519.
[38] B. Wrackmeyer, Annu. Rep. NMR Spectrosc. 16 (1985) 73.
[39] V.J. Hall, E.R.T. Tiekink, Main Group Met. Chem. 21 (1998)
245.
[40] V.J. Hall, E.R.T. Tiekink, Main Group Met. Chem. 18 (1995)
611.
[1] T. Jiang, G.A. Ozin, J. Mater. Chem. 8 (1998) 1099.
[2] R. Hertzenberg, Rev. Minerals 4 (1932) 33.
[3] B. Polosz, W. Steurer, H. Schultz, Acta Crystallogr., Sect. B 46
(1990) 449.
[4] M. Hell, Ger. Offen. DE 4,340,017 (Cl.C08J5/14), 1 June, 1995.
[5] M. Geringer, PCT Int. Appl. WO 96 36,681 (Cl.C/O M 103/06),
21 November, 1996.
[6] H.P. Rimmington, A.A. Balchin, J. Cryst. Growth 15 (1972) 51.
[7] I. Oftedal, Z. Phys. Chem. 134 (1928) 301.
[8] R. Kneip, D. Mootz, U. Severin, H. Wunderlich, Acta Crystal-
logr., Sect. B 38 (1982) 2022.
[9] P. Boudjouk, D.J. Seidler, S.R. Bahr, G.J. McCarthey, Chem.
Mater. 6 (1994) 2108.
[10] M.B. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 10 (1967)
247.
[41] J.M. Hook, B.M. Linahan, R.L. Taylor, E.R.T. Tiekink, L. van
Gorkom, L.K. Webster, Main Group Met. Chem. 17 (1994) 293.
[42] D. Dakternieks, H. Zhu, D. Masi, C. Mealli, Inorg. Chem. 31
(1992) 3601.
[11] K. Deraman, S. Sakrani, B. Bismail, Y. Wahab, R.D. Gould,
Int. J. Electronics 76 (1994) 917.
[43] K. Kim, J.A. Ibers, O.-S. Jung, Y.S. Sohn, Acta Crystallogr.,
Sect. C C43 (1987) 2317.
[12] G.B. Dubrovski, N.S. Zhdanovich, Fiz. Tverd. Tela (Leningrad)
38 (1996) 272.
[44] E. Kello¨, V. Vrabel, I. Skacani, Acta Crystallogr., Sect. C: Cryst.
Struct. Commun. 51 (1995) 408.
[13] J.P. Singh, R.K. Bedi, Thin Solid Films 199 (1991) 9.
[14] A. Ortiz, J.C. Alonso, M. Garcia, J. Toriz, J. Semicond. Sci.
Technol. 11 (1996) 243.
[45] P.F. Lindley, P. Carr, J. Cryst. Molec. Struct. 4 (1974) 173.
[46] T.G. Hibbert, M.F. Mahon, K.C. Molloy, Main Group Met.
Chem. 22 (1999) 235.